I always thought Bill Duke from X3 was supposed to be Apocalypse hiding in plain sight. I mean...until the end of the movie. But they could still do that. Easy fix: President calls him Secretary Trask once right? So have him be playing a guy who influenced Trask Industries after Bolivar died or something and the President sarcastically called him "Secretary Trask here" as a jab. Come DOFP and he helped initiate the Sentinels or whatever. That's probably too over the top but I think he fits the role.